Known internal combustion engines for vehicles comprise a head bearing one or more cylinders, inside which the engine cycle is carried out, and which communicate with respective combustion chambers of the engine. On the aforesaid head there are also provided suitable seats for connecting the combustion chamber with ducts suitable for supplying said chamber with a mixture of unburnt fuel and air (“intake ducts”) and for removing the combusted gases from said combustion chamber (“exhaust ducts”).
The flows from and towards each combustion chamber are controlled by suitable valves acting on the aforesaid seats. In particular, each valve essentially comprises a guide element, fixed inside a cavity of the head of the engine and defining a through seat, and a stem, slidingly movable in opposite directions within the aforesaid seat and carrying at one end a shuttering element to close the connection between the relative intake or exhaust duct and the corresponding combustion chamber.
The opposite end of the valve stem axially projects from the respective guide element and receives actuating forces from a relative control device, for example a cam shaft.
The valve stem is axially loaded by a helical spring in the closing direction of the connection between the respective intake or exhaust duct and the corresponding combustion chamber.
In particular, the spring is coaxially mounted about the valve and is axially interposed between a stationary surface formed on the head of the engine and a plate fastened to the valve stem, near or at the end of the stem cooperating with the control device.
The valves of the aforesaid type normally have sealing gaskets for the lubricating oil normally circulating in the engines. Said gaskets, in one of the most commonly known forms, comprise a support or reinforcement member, having a substantially tubular shape and made of a single piece of metal material, and an annular sealing element, made of elastomeric material and interposed between the support element and the valve.
In particular, the sealing element typically comprises a first portion cooperating through its own radially inner annular surface with the radially outer annular surface of the portion of the guide element oriented in use towards the aforesaid control device, and a second portion directly cooperating with the valve stem.
The gaskets of the aforesaid type are widely used on all internal combustion engines to control the amount of lubricating oil flowing from the distribution area to the combustion chambers. An excessive flow of lubricating oil causes, besides an obviously high oil consumption, a deterioration of the efficiency of the engine and a reduction in the performance of the catalyst of the vehicle. On the other hand, an insufficient flow causes increased wear and noise of the valves together with local temperature peaks. These phenomena can cause a premature damage to the valves due to the seizure of the valve stem inside the guide element.
Thanks to the first portion of the sealing element acting on the guide element of the relative valve, the known sealing gaskets allow a static type seal, and thanks to the second portion of the sealing element cooperating with the stem, a dynamic type seal. In particular, the static seal must ensure a certain degree of radial compression on the guide element in order to avoid the leakage of lubricating oil towards the combustion chambers and at the same time keep the gasket in position, while the dynamic seal is designed for allowing the minimum flow of oil necessary for the lubrication of the coupling between the stem and the guide element.
The support element includes:                a main portion substantially shaped like a cylindrical sleeve cooperating along its entire axial height with the sealing element;        a first annular flange extending radially inwardly from an axial end of the main portion and partly embedded in an annular seat of the sealing element; and        a second annular flange extending radially outwardly from an opposite axial end of the main portion and suitable to be pushed against the aforesaid stationary surface of the head of the motor by the spring acting on the valve stem. The second annular flange of the support element defines an abutment surface for an axial end of the spring and receives from this latter the normal operating loads.        
The second annular flange also allows the gasket to be actuated in the desired position on the valve.
An example of an aforesaid type of gasket is disclosed in the Italian patent for utility model no. 0000281466.
The disclosed solution, although functionally valid, is susceptible of further improvements, in particular as regards the evacuation of the heat generated inside the gasket during the valve operation.